1. Field
Embodiments relate to an apparatus and a method for generating pulsatile flows having a wave functional form, and more particularly, to an apparatus and a method for generating pulsatile flows, which rotates a liquid vessel at a constant angular velocity by means of a plurality of rotating disks operating in association with each other and implements revolution based on Fourier cosine series and a principle of hydraulic head difference associated with the Bernoulli concept in relation to a pressure difference, thereby generating a periodic pressure difference of a wave functional form by the change of height of a liquid surface.
2. Description of the Related Art
The pulsatile flow is a term in the field of fluid mechanics and refers to all kinds of flows having a periodic change with respect to a flow velocity. Most representatively, the pulsatile flow is a flow of blood in a blood vessel, caused by periodic shrinkage and release of the heart. In the engineering fields, most pumping devices except for a syringe pump or the like exhibit the pulsatile flow. In the field of microfluidics which gives a great influence on the development of next-generation bio-medical techniques such as an high-precision micro pump, the role of the pulsatile flow is greatly increased. But there are many limits in aspect of precise implementation, efficient operation, and manufacture costs. The flow of liquid may not be easily interrupted or controlled instantly due to the inertia of the fluid, different from electric current, even though the amount of liquid is small. A pumping device generating a pulsatile flow has been initially used for extracorporeal circulation of blood during a heart surgery. For example, Basiglio and Vergamo (Basiglio, R. F., Vergamo, L. P., U.S. Pat. No. 5,044,901, entitled “Pulsatile pump for extro-corporeal circulation”, September, 1991) have invented a pulsatile pump for extracorporeal circulation.
Fourier cosine series is a technique for approximately expressing any even function given as a time periodic function using a linear combination of cosine functions which are representative periodic even functions. In this regard, Fourier sine series is used for approximating an odd function to a sine function, and Fourier series is also used for approximating a function other than an even function or an odd function to a cosine or sine function. Herein, the oscillation frequency of the sine or cosine function is given as an inverse number of integer multiple of pi. Meanwhile, when approximating a function other than a periodic function, Fourier transform is used, and in this case the oscillation frequency is a real number space.
The microfluidics deals with the fluid flowing through a microchannel formed in a microfluidic chip, and recently plays an important role in the bio-MEMS and power-MEMS. In a microfluidic device, a pressure-driven device such as a pump is frequently used to maintain a normal fluid flow or apply a periodic/non-periodic velocity change. However, the pump has a very large size in comparison to the microfluidic chip, which disturbs miniaturization of a system. In addition, if precise flow control is required, the costs and components for a demanded pump are greatly increasing. Melin and Quake (Melin, J., Quake, S. R., “Microfluidic large-scale integration: The evolution of design rules for biological automation”, Annu. Rev. Biophys. Biomol. Struct., 36, 213-31, 2007) have invented a method for embedding a micro pump in a microfluidic chip, but a complicated external pressurizing device is required to operate the embedded pump.
A square wave, which is a kind of the wave function, may be ideally obtained only at a very rapid response according to opening/closing of an electric current, like an electronic circuit or signal processing. It is practically very difficult to perfectly implement a square wave pulsatile flow in which fluids having two different flow rates change periodically or instantly. When a drug delivery matrix or a batch-type microreactor is implemented in a microfluidic chip, a pulsatile flow of a square wave form is needed. In most cases, expensive wave-controlling syringe pumps commercially available are used instead, but these have an obvious limit in implementing the square wave.
Kim et al. (Kim, D., Chester, N.C., Beebe, D. J., “A method for dynamic system characterization using hydraulic series resistance”, Lab Chip, 6, 639-644, 2006) have attempted to implement a square wave pressure difference in a microfluidic channel by using a complicated device design including a sensor, a computer controller, a regulator or the like. However, due to the serious complexity of the device, there is a limit in accuracy, and for example, an actually implemented result deviates from a theoretical input value according to the size of the channel. In addition, in this device, only a forwarding type pulsatile flow may be implemented.
Lee et al. (Lee, Y. S., Oh, Y. S., Kuk, K., Kim, M. S., Shin, S. J., Shin, S. H., “Micro-pump driven by phase change of a fluid”, US Patent Publication No. 2004/0146409, January, 2004) have invented a device for instantly increasing a flow rate supplied to a micro channel, by using a phase change of fluid by heat. However, the pulsatile flow generated in this way is also used for inducing a cascade-type flow and is not suitable for generating a back-and-forth standing type pulsatile flow.